Impeller

ABSTRACT

A pressure boost impeller configured for compressing fluids, such as gases and liquids. Such impeller has a front intake area and a rear discharge area, and a hub containing the rotational axis of the impeller. Several blades extend about the hub, with some of the blades being in an overlapping relationship to define a passageway between adjacent blades. The passageway has an inlet communicating with the front intake area and an outlet communicating with the rear discharge area. The inlet is greater in area than the outlet, thus defining a step down in volume of fluid passing through the passageway.

TECHNICAL FIELD

This invention relates to an impeller and especially to a pressure boostimpeller suitable for compressing fluids such as gases and liquids.

BACKGROUND ART

Known impellers or fans can include an arrangement of airfoils. Byairfoils is meant a foil or blade which is substantially a version of awing. A typical wing or foil has a shape which creates a greaterdistance over one side, which is usually the topside, than the oppositeside.

This configuration of a typical foil or wing when driven forward withits thickest end foremost splits the ambient fluid, be it gases orliquids to cause a portion to pass over the top and a portion to passunderneath. The greater distance the fluid travels over the side withthe greatest curve, which is usually the top, forces that fluid to atendency toward being attenuated.

This substantial attenuation causes a lowering of pressure. The loweredpressure attracts adjacent fluid and the effect is to create an upwardsuction. If the wing or foil cannot rise, the fluid travels down to meetit and usually passes mostly behind the trailing edge.

In this type of foil or wing it can be seen that there is a directrelationship between each side of the wing or foil.

If, because of a too coarse pitch (nose up) the pressure underneathbecomes too high and the pressure above becomes too low, the foil orwing will stall. In this case the high pressure fluid from the undersidecreeps around the Trailing edge and forward along the topside and causesdetachment of the topside fluid flow. Upwards suction is lost or greatlydiminished and therefore loss of lift occurs.

High pressure air also travels around the foil or wing tips and createsvortices, which detracts from lift and creates a drag on the foil nearits tips.

A typical conventional fan is almost always a circular arrangement ofthese foils or small wings and is subject to the same factors whichcause a loss of efficiency.

In a typical conventional radial flow fan, the foils or miniature wingsdiverge from each other from a medial to a lateral area. In thissituation, each foil or wing relies on the lower pressure air travellingover the low pressure side of the foil or wing to substantially reachthe trailing edged to rejoin the higher pressure air being flungradially by the high pressure side of the foil. So in this type of fanis subject to having its blades or foils stall if a back pressure orhead pressure is generated. If this type of fan is driven to too hightip speed each foil stalls and in certain circumstances fluid canactually travel back between each set of foils along the low or suctionside of the foils. In effect there is created a counter current of fluidbetween any two foils.

DISCLOSURE OF THE INVENTION

It is an object of the invention to provide an impeller which maysubstantially overcome the abovementioned disadvantages or provide thepublic with a useful or commercial choice.

In one form, the invention resides in an impeller having a front intakearea and a rear discharge area, a hub containing the rotational axis ofthe impeller, a plurality of blades extending about the hub, at leastsome of the blades being in an overlapping relationship to define apassageway between adjacent overlapping blades, the passageway having aninlet communicating with the front intake area, and an outletcommunicating with the rear discharge-area, the inlet having an arealarger than the area of the outlet to define a step down in volume offluid passing through the passageway.

The blades extending about the hub may have a leading edge which candefine part of the inlet, a trailing edge which can define part of theoutlet, an outwardly extending tip, and a root which can be attached tothe hub.

The blades can be attached to the hub at a distance spaced from therotational axis to define a land portion between the blades and therotational axis. This land portion can cover between 10% to 50% of thearea of the hub, and typically comprises at least 30%. The root of theblades can be attached to the hub adjacent the rear discharge area.

The blades may have an airfoil configuration whereby the leading edgecan be thickened relative to the trailing edge and whereby incomingfluid can be split to cause a portion of the fluid to pass over one sideof the blade, and a portion of the fluid to pass on the other side ofthe blade. Due to the airfoil configuration, fluid passing over one sideof the blade must travel along a longer pathway than fluid passing alongthe other side of the blade which causes attenuation of the fluid. Theblades may be curved between the leading edge and the trailing edge andtherefore adjacent blades may be in a curved overlapping relationship.

The hub may be substantially cone-like in configuration and may divergefrom the intake area to the discharge area. The blades may be attachedto the cone shaped hub. The discharge area of the hub may besubstantially planar.

At least some of the blades, and preferably all of the blades may beangled outwardly relative to the rotational axis. Thus, a line definedbetween the root and tip of a particular blade may diverge from therotational axis of the hub.

Although the degree of overlap between adjacent blades may vary, it ispreferred that the overlap is at least 50% to allow the desiredpassageway to be formed.

To achieve the step down in volume between the inlet and the outlet ofthe passageway, the adjacent blades defining the passageway may convergerelative to each other from the leading edge to the trailing edge. Theleading edge and the trailing edge of each adjacent blade may besubstantially the same length, with the convergence of the bladesresulting in the step down in volume along the passageway. The adjacentblades may be of a rigid construction and may be fixed in the desiredconverging position.

Alternatively, the degree of convergence may be varied either beforeand/or during rotation of the impeller. Thus, the blades may bepivotally mounted adjacent their leading edges to allow the blades topivotally move towards an adjacent blade. Alternatively, or in additionto the above, some or all of the blades may be flexible, or comprise aflexible portion which can alter the shape of the blade to allow it toconverge relative to the adjacent blade.

In a further alternative, the step down in volume may be achieved byhaving the leading edges of an adjacent pair of blades longer than thetrailing edges of the same adjacent pair of blades. In this alternative,the tip of each blade can taper from the leading edge to the trailingedge. The blades may be substantially parallel and need not converge,although they do if desired. Indeed, depending on the ratio between theleading edge length and the trailing edge length, the blades may evendiverge while still providing a step down in volume.

It is also desirable to have the intake area larger than the inlet areaof the passageways. Thus, the intake area may be defined by the junctionof the leading edge and the tip of each blade. If the blades are angledoutwardly from the rotation axis, the intake area (ie. eye or throatarea) can be considerably larger than the inlet area (ie. blade sweptarea).

The impeller can be fitted to a rotating shaft and can be mounted withina shroud or housing, with the tips of each blade being sealinglyengagable with the shroud or housing, or being closely spaced therefrom.The shroud or housing may be concave in configuration to encompass theimpeller.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a plan view of an impeller according to the invention.

FIG. 2 is a side view of the impeller of FIG. 1.

FIG. 3 is a representation of fluid flowing past adjacent blades of theimpeller.

FIG. 4 is a schematic view of a two passageway impeller according to anembodiment of the invention.

FIG. 5 is a schematic view of a prior art two bladed radial flow fan.

FIG. 6 is a schematic view of pivotal blades of an impeller according tothe invention.

FIGS. 7 and 8 are rear and front views of an impeller according to afurther embodiment of the invention.

FIG. 9 is a table showing various parameters of the impeller of FIG. 1.

FIG. 10 is a graphical representation of the results of the table inFIG. 9.

BEST MODE

Referring to the drawings and initially to FIG. 1 there is shown animpeller 10. Impeller 10 can be formed from metal (although need not belimited to such), and comprises a central hub 11 and a plurality ofblades 12. Impeller 10 also includes an intake area shown by dotted line13 and which can be defined by the junction of a leading edge 14 and atip 15 of a particular blade 12. Each blade 12 includes a leading edge14 which communicates with intake area 13, an outwardly extending tip15, a root 16 by which the blade is attached to hub 11, and a trailingedge 17 which communicates with a discharge area 18 (see FIG. 2) ofimpeller 10. Hub 11 has a central rotational axis 19, and in FIG. 1 hub11 includes a central bore 20 so that impeller 10 can be mounted to ashaft (not shown) for rotation therewith.

Blades 12, 12a are in an at least partially overlapping relationship todefine a passageway 21 extending between the pair of adjacent blades 12,12a. The adjacent blades have an overlap area of between 30 to 70percent to ensure the existence of a reasonably sized passageway 21.

The blades on hub 11 diverge outwardly relative to the rotational axis19 as shown in FIG. 1. This outward divergence results in a large intakearea 13. This can be achieved by having hub 11 cone-like inconfiguration as illustrated in FIG. 2, with the hub diverging from anarrower portion adjacent the front intake area to a broader portionextending to the rear discharge area. By having blades 12 mountedsubstantially at right angles to the inclined cone-like surface of hub11, the blades will adopt the divergent position shown in FIGS. 1 and 2.

The root of each blade is attached to the hub at a positionsubstantially spaced from the rotational axis, to give hub 11 a landportion 22 (see FIG. 1) extending between the rotational axis 19, orbore 20 and the root of each blade. The land portion may comprisebetween 20 to 60 percent of the surface area of the hub. That is, blades12 do not extend all the way towards either the rotational axis 19 orbore 20.

FIG. 2 shows in dotted outline 23 the discharge area, or outlet 24 ofeach passageway defined between an adjacent pair of blades.

Referring to FIG. 3, it can be seen that the blades have an airfoil typeconfiguration comprising a thickened leading edge 14, 14a and a thinnertrailing edge 17, 17a. The airfoil configuration of each blade, resultsin the fluid being split by a respective leading edge 14, 14a into aportion which flows over an upper side of the blade 25 and a portionthat flows over the lower side of the blade 26. The lower side 26,defines a longer pathway for the fluid to travel, and this causes areduction in pressure of the fluid on surface 26 relative to surface 25.

When impeller 10 is rotated, the incoming fluid is compressed againstupper side 25 (as shown in FIG. 3). At the same time, fluid on the lowerside 26 is decompressed, rarified or attenuated causing a reduction inpressure. As the fluid is compressed and travels along upper surface 25of each blade, if the trailing edge of the adjacent blade is spaced fromupper surface 25 by a distance approximating the thickness of thecompressed fluid passing along upper surface 25, then there is asubstantial reduction in the tendency of the fluid to flow backwardsalong the low pressure side of the blade.

Thus, as shown in FIG. 3, adjacent blades converge relative to eachother between their leading edges and trailing edges, with the distancebetween the trailing edge 17 of one blade between upper surface 25 of anadjacent blade approximating the "thickness" of the high pressure fluidflowing through passageway 21 and along the upper surface 25 of theblade.

As the fluid is driven into a high pressure area adjacent the dischargeare 18, the head pressure in this area is exerted substantiallyperpendicular to the inflow direction of the fluid passing into thehigher pressure area. This is illustrated as numeral 27 in FIG. 3 whichshows that as high pressure fluid passes through outlet 24, the headpressure in the discharge area (for instance a compression tank) doesnot exert itself totally against the flow but substantiallyperpendicular to the flow.

Only when the energy found as pressure and or velocity of the incominggases is exceeded by the energy found as pressure of the gases adjacentthe member trailing edges (as in a plenum chamber or pressure vessel)can the inflow be substantially disturbed or prevented.

With fixed pitch members this ability of the impeller 10 to compressgases is found within a relatively narrow speed range.

As liquids are substantially incompressible, the degree of said memberconvergence need only be to the extent of adjusting at the design pointa situation where the impeller 10 inflow side is approximately the sameas the outflow side for almost any R.P.M.

FIG. 6 illustrates three representative airfoil shaped blades 12, 12a,12b which are pivotally mounted through pivot points 28 to the hub (notshown). The pivot points being adjacent the leading edges 14, 14a, 14b.During rotation of the impeller in the direction of arrow illustrated inFIG. 6, these blades can be self tuning with the trailing edges beingautomatically positioned away from the upper surface of an adjacentblade by the approximate thickness of the high pressure fluid flowflowing across the upper surface. This self alignment is caused by thehigh pressure fluid flow on the upper surface of each of the blades 12,12a, 12b tending to pivot the blade towards the upper surface of anadjacent blade, with the high pressure fluid on the adjacent bladelimiting the degree of pivoting movement. This self tuning or selfadjusting effect can also be achieved by having the blades formed fromflexible material, or a portion of the blade adjacent the trailing edgebeing formed from flexible material which can then deform to be selfadjusting.

FIGS. 4 and 5 illustrate the significant difference between a prior artradial fan employing only two blades (FIG. 5) with an impeller accordingto an embodiment of the invention employing two passageways (FIG. 4).With the prior art fan of FIG. 5, the area between each blade 30, 31performs no function. In FIG. 4, the impeller is shown as solid material32, 33 which performs no function between the passageways 34, 35 andthis shows that with the impeller the work is performed between any twoof the blades and that the relationship is between the high pressureside of one blade and the low pressure side of an adjacent blade. In thecase of a conventional radial flow fan employing airfoil shaped blades,the work of transporting the fluid is performed substantially along thefull length of both sides of the blade. With the impeller the work ofcompressing and transporting the fluid is performed substantiallybetween the leading edge of each blade and a trailing edge of anadjacent blade.

FIGS. 7 and 8 illustrate an alternative embodiment of the impellor. Inthis embodiment, impellor 40 includes a hub 41 similar to that describedearlier, the hub having a bore 42 to allow the impellor to be mounted toa shaft. A plurality of blades 44a, 44b are spaced about a peripheralarea of the impellor, and are mounted to hub 41. Blades 44a, 44b are ina spaced overlapping configuration to define a passageway 45 between anadjacent pair of overlapping blades (ie. 44a, 44b). Passageway 45 has aninlet and an outlet similar to that described above, and also has a stepdown in volume between the inlet and the outlet by having the leadingedge 46a, 46b of each respective blade longer than the trailing edge47a, 47b. Thus, passageway 45 tapers downwardly from the inlet to theoutlet of passageway. Depending on the length of the leading edges tothe trailing edges, adjacent blades 44a, 44b need not converge, but maybe in a curved parallel relationship, or even slightly divergent whilestill providing the step down in volume.

Some versions of the impeller may when viewed from the side, possessblades which are arranged at angles other than parallel to a line whichis at right angle (90°) to the axis. There are advantages in this incertain circumstances. For example when comparing this angled bladeconfiguration of the impeller with a conventional radial flow fan it canbe seed that the eye or fluid intake face of the impeller is much largerthan the eye of a conventional radial flow fan. It can also be seen thatthe said blade swept area of the impeller is much larger than the bladeswept area of the conventional radial flow flan.

The angled blade version of the impeller also makes it possible to morereadily turn the fluid after it has passed through the impeller into anaxial direction while still having taken advantage of the centrifugaleffect common to a radial flow fan or the impeller. Versions of theimpeller with angled blades as described may also feature the convergingblades already described. The tips 15 of the blades of the impeller aremeant to pass closely by a shroud. This shroud is not shown in any ofthe drawings for clarity.

FIGS. 9 and 10 illustrate a table, and in graphical form the advantagesof the impeller. The information indicates that the impeller resistsstall and can maintain high static pressure at very low flow rates. Theimpeller does not follow the traditional fan curve illustrated instandard handbooks.

A typical centrifugal type compressor may possess blades or airfoilsthat do overlap, however those blades diverge from a medial towards aperipheral area whereas the blades of the impeller may converge.

A centrifugal type compressor relies on a gas velocity change to achievecompression. Gas is drawn into a relatively small eye, undergoes adirection change from axial to radial and is flung outwardly at highvelocity. In this type of compressor the highest gas velocity isachieved as it comes off the blade trailing edges. This high velocitygas is almost immediately reduced in velocity and undergoes a pressurerise. In the centrifugal type compressor the pressure gain is relativelysmall.

Note that in the centrifugal type compressor, gases are first compressedagainst the advancing high pressure side of each blade or foil. Thegases then undergo a reduction in pressure as they are flung off theblade tips at high velocity. They then undergo a pressure increase astheir velocity is reduced. This rapid change in velocity and pressurecontributes to inefficiency.

The impeller in having the said blades placed more peripherally and insuch a manner as to maximise compression of gases against the advancinghigh pressure side of the blades, achieves the desired high pressurerise between the said blades and does not produce the subsequentpressure reduction and pressure increase of the gases after leaving theblades as does the centrifugal compressor.

Stated another way: The impeller achieves the desired pressure risebetween the members or more specifically between the leading edge of agiven blade and the trailing edge of the preceding blade. In this waythe angled member version of the impeller minimises gas directionchange: offers increased eye or gas intake area: and achieves theobjective of gas compression in substantially one action instead ofthree abrupt velocity and pressure changes as in the centrifugal typecompressor. It is to be noted that typical axial flow compressorsachieve compression by the same means of velocity reduction as docentrifugal compressors and both are subject to blade or airfoil stall;a problem which the impeller substantially reduces. Also note that thelarge eye or fluid intake face of the angled blade versions of theimpeller may take advantage of the ram effect when used in place of aconventional forward moving ducted fan or axial flow compressors.

The impeller can be used in place of underwater propellers. The bladesof the impeller may be at any angle relative to the plate-like orcone-like hub. The cone-like hub may be at any cone angle.

The cone-like hub and said blade tips may possess a radius. The bladesof the impeller may have a twist when viewed from any angle.

The blade of the impeller may possess a radius that alters along theirlength.

The blades of the impeller may possess a constant thickness or a sharpleading edge and or trailing edge.

The blade of the impeller when viewed from the side may have their rootand tip angles the same or different relative to each other.

What is claimed is:
 1. An impeller having a front intake area and a reardischarge area, a hub containing a rotational axis of the impeller, aplurality of blades extending about the hub, at least some of the bladesbeing in an overlapping relationship to define a passageway betweenadjacent overlapping blades, the passageway having an inlet defined by aleading edge of each adjacent blade and communicating with the frontintake area, and an outlet defined by a trailing edge of each adjacentblade and communicating with the rear discharge area, wherein each bladeis curved to define an outer convex side and an inner concave side, theouter convex side adapted to impact against and compress fluid as theimpeller rotates, each blade further having a lower root edge and anupper free tip edge, the adjacent overlapping blades converging towardseach other from the inlet to the outlet, the leading and trailing edgesof each blade diverging outwardly from the rotational axis.
 2. Theimpeller as claimed in claim 1, wherein the blades are spaced from therotational axis of the hub to define a land portion between therotational axis and one of said blades.
 3. The impeller as claimed inclaim 2, wherein the land portion comprises at least 30% of the area ofthe hub.
 4. The impeller as claimed in claim 3, wherein the blades areattached to the hub adjacent the discharge area.
 5. The impeller asclaimed in claim 2, where The blades have an airfoil configuration fromthe leading edge to the trailing edge.
 6. The impeller as claimed inclaim 1, wherein the hub is substantially cone shaped and diverges fromthe intake area to the discharge area.
 7. The impeller as claimed inclaim 1, wherein the degree of overlap between adjacent blades is atleast 30%.
 8. The impeller as claimed in claim 1, wherein the blades arefixed in the converging position.
 9. The impeller as claimed in claim 1,wherein the intake area is larger than the inlet area of one of saidpassageways such that a step down in volume is achieved between theintake area and the inlet area.
 10. The impeller as claimed in claim 1,wherein said impeller is a fluid compressor impeller.